全文获取类型
收费全文 | 40657篇 |
免费 | 7009篇 |
国内免费 | 6442篇 |
专业分类
化学 | 31555篇 |
晶体学 | 610篇 |
力学 | 1944篇 |
综合类 | 549篇 |
数学 | 4511篇 |
物理学 | 14939篇 |
出版年
2024年 | 139篇 |
2023年 | 742篇 |
2022年 | 1376篇 |
2021年 | 1443篇 |
2020年 | 1615篇 |
2019年 | 1679篇 |
2018年 | 1442篇 |
2017年 | 1461篇 |
2016年 | 2033篇 |
2015年 | 2132篇 |
2014年 | 2516篇 |
2013年 | 3177篇 |
2012年 | 3705篇 |
2011年 | 3856篇 |
2010年 | 2880篇 |
2009年 | 2794篇 |
2008年 | 2964篇 |
2007年 | 2702篇 |
2006年 | 2577篇 |
2005年 | 2149篇 |
2004年 | 1617篇 |
2003年 | 1327篇 |
2002年 | 1328篇 |
2001年 | 1083篇 |
2000年 | 969篇 |
1999年 | 788篇 |
1998年 | 542篇 |
1997年 | 482篇 |
1996年 | 431篇 |
1995年 | 386篇 |
1994年 | 350篇 |
1993年 | 258篇 |
1992年 | 212篇 |
1991年 | 184篇 |
1990年 | 163篇 |
1989年 | 125篇 |
1988年 | 96篇 |
1987年 | 79篇 |
1986年 | 81篇 |
1985年 | 67篇 |
1984年 | 27篇 |
1983年 | 26篇 |
1982年 | 24篇 |
1981年 | 12篇 |
1980年 | 11篇 |
1979年 | 10篇 |
1973年 | 6篇 |
1971年 | 5篇 |
1957年 | 8篇 |
1936年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
报道了KDP晶体中的三倍频产生的实验研究,计算了比较了直接三倍频过程和级联过程对KDP晶体三阶有效非线性系数的贡献,并探讨了KDP作为非线性晶体材料三阶非线性系数测量基准的可行性。 相似文献
42.
43.
44.
双线性系统的无反馈解耦线性化 总被引:1,自引:1,他引:0
严星刚 《纯粹数学与应用数学》1995,11(2):21-28
用现代微分几何方法研究了双线性控制系统的解耦线性化问题,给出了一般双线性系统解耦线性化的充分条件及严格双线性系统解耦线性化的充要条件,并举例说明了本文的结论。 相似文献
45.
Wang Dunhui Huang Songling Han Zhida Su Zhenghua Wang Yi Du Youwei 《Solid State Communications》2004,131(2):97-99
A series of Gd(1−x)Bx alloys have been prepared by arc melting method. After introducing small quantity of B atom in Gd, the Curie temperature of these alloys increase while the magnetic entropy changes are almost same as that of Gd. The refrigerant capacities of these alloys are also greater than that of Gd. These results suggest that Gd(1−x)Bx alloys may be utilized as refrigerant in household magnetic refrigeration. 相似文献
46.
Imaging mass spectrometry requires the acquisition and interpretation of hundreds to thousands of individual spectra in order to map the mineral phases within heterogeneous geomatrices. A fuzzy logic inference engine (FLIE) was developed to automate data interpretation. To evaluate the strengths and limitations of FLIE, the chemical images obtained using FLIE were compared with those developed using two chemometric methods: principle component analysis (PCA) and cluster analysis (K-Means). Two heterogeneous geomatrices, a low-grade chalcopyrite ore and basalt, were imaged using a laser-desorption Fourier transform mass spectrometer. Similar mineral distribution patterns in the chalcopyrite ore sample were obtained by the three data analysis methods with most of the differences occurring at the interfaces between mineral phases. PCA missed one minor mineral phase in the chalcopyrite ore sample and did not clearly differentiate among the mineral classes of the basalt. K-Means cluster analysis differentiated among the various mineral phases in both samples, but improperly grouped some spectra in the chalcopyrite sample that only contained unanticipated high mass peaks. Unlike the chemometric methods, FLIE was able to classify spectra as unknowns for those spectra that fell below the confidence level threshold. A nearest neighbor approach, included in FLIE, was used to classify the unknowns to form a visually complete image; however, the unknowns identified by FLIE can be informative because they highlight potential problems or overlooked results. In conclusion, this study validated the fuzzy logic-based approach used in our laboratory and reveald some limitations in the three techniques that were evaluated. 相似文献
47.
48.
49.
50.
In this paper a half space problem for the one-dimensional Boltzmann equation with specular reflective boundary condition is investigated. It is shown that the solution of the Boltzmann equation time-asymptotically converges to a global Maxwellian under some initial conditions. Furthermore, a time-decay rate is also obtained. 相似文献